Saturday, July 7, 2012

Urban pedestrian projects

Walking Paris day after day gives an opportunity to acquire a deeper familiarity with the city. It takes a long time to get to know a street, and, even without paying attention to the people, I can walk it many times without exhausting its riches. Here are some of the angles that the wandering mind sometimes takes, depending on the day's mood. I have a feeling that they bear the mark of a scientific training, and that a, say, literature major, walking along the same streets and looking at the same buildings, would see completely different things.

Inside and outside plans. Infer the internal organization of a building from the outside setup of doors and windows. Where is the staircase? How many apartments are there? Where are the separations between apartments? Much of the building plan can be guessed from examining the disposition of the windows.

Ceiling heights. It happens that adjacent buildings have the same height yet a different number of floors: one has 7 floors, the one next to it has 8 floors, yet their roofs are lines up. Why? Because the floors have different heights. Correlate floor height to the age of the buildings.

Symmetry and near-symmetry. Find perfectly symmetrical patterns. Find patterns that are not symmetrical. Why not? Are those departures from perfect symmetry accidental or voluntary? Example: The central column of Notre Dame's facade, the tip of the roof behind it, and the tall steeple in the back, are not quite lined up, thus missing an opportunity for pleasing symmetry.

Friday, July 6, 2012

A tradition that deserves to die

How do you know whether you have been accepted to your dream college or university?

Yesterday I heard a microphone in the cloister-like courtyard outside my office. There was a small crowd around a man who was saying slowly, articulating carefully: "... Third: David Smith. [Sound of hands clapping]. Fourth: Jane Doe. [Sound of hands clapping]...": he was publicly proclaiming the results (in the humanities) of the entrance exam of Ecole Normale Superieure!

A few minutes later, I walked across the yard and saw people scattered about, some with a big smile on their face, others crying. Many people were on the phone.

I wonder: Results and rankings are public in France: they are published in the newspapers, and grades are posted on bulletin boards outside schools. But this ceremonial in the historical courtyard goes one more step towards delivering praise and humiliation, and maximizes anxiety among candidates. Could this setup be considered a form of hazing?

Thursday, July 5, 2012


Days before a conference deadline (SODA, for this week) are marked by increasing intensity of work, gradually setting aside more secondary tasks as the deadline nears. I used to have a surge of adrenaline on the day of the deadline: now I'm just impatient with myself for not having tied loose ends much earlier.

Day after the conference deadline: goofing off.

Day after the day after the conference deadline: cleaning up. Taking stock of all the urgent tasks that got shoved aside to make room for the conference submission, apologizing for things that were not done and people who were ignored, and working at getting things back under control.

Almost every computer scientist I know works in that way. Almost none of the mathematicians or physicists I know work in that way. Why have we chosen such a stressful and unpleasant way of organizing our work? More importantly, why is it so hard to break the habit? Part of the reason is that the minority rules in that case: in a group of collaborators, it is enough that one person works in that mode to force all participants to adopt it. In the DAG of tasks that need to be done, as long as a few critical tasks belong to a person of that culture, all members of the project have to also follow the same pattern of behavior, I think.

So what can be done to change behavior? Getting rid of hard deadlines would change the way the field works. One possible direction is the possibility of rolling deadlines.

Sunday, July 1, 2012

The small world phenomenon

Recently by coincidence I learned that one of my dad's friends from old times was the friend of a friend of a friend of a friend. It's a cycle of length 6. Such cycles are probably quite common, but how easy is it to detect them when there are no shortcuts? Another way to phrase this: how can I discover the people who are at distance 3 from me but have at least 2 paths from me to them? Distance 2 seems feasible: as I chat with my friends, they often tell me about their own friends, so I know a little bit about my friends' friends, and so I can with reasonable chance discover cycles of length 4. But I know nothing about my friends' friends' friends...